1. Field of the Invention
The present invention relates to an illumination module of light emitting elements, and more particularly to an illumination module of light emitting elements utilized in a backlight system.
2. Description of the Prior Art
In recent years, so-called liquid crystal display devices using liquid crystal panels have been widely used as display devices, which serve as monitors for image reproducing apparatus or various information terminals.
In general, such a liquid crystal display device uses a passive matrix type of liquid crystal panel or an active matrix type of liquid crystal panel using non-linear devices. These types of liquid crystal panel are not of the self light emitting type, and so they require an illumination light source to form a visible image formed on the liquid crystal panel. Liquid crystal panels are divided into a transmission type and a reflection type. In monitors for information terminals, the transmission type of liquid crystal panel is widely used for the purpose of high-luminance and high-contrast display, and for this purpose a backlighting illumination light source (hereinafter referred to as a backlight) is installed on the back of the liquid crystal panel, and a visible image is formed by modulating light from this backlight to form an image on the liquid crystal panel.
FIG. 1 is a cross-sectional view illustrating an example of a conventional liquid crystal display device provided with a transmission type of liquid crystal panel and a backlighting illumination device, i.e. a so-called backlight, associated with an illumination source of light emitting diodes. The conventional liquid crystal device has a backlight stacked on the back of the transmission type of liquid crystal panel, and is constructed to modulate, with an image formed on the liquid crystal panel, illumination light which is emitted from the backlight and which passes through the liquid crystal panel. The modulated illumination light is caused to exit toward the observer side of the liquid crystal panel, thereby making the image visible.
Specifically, this kind of liquid crystal display device is constructed in the following manner, as seen in FIG. 1. In a liquid crystal panel 1, a liquid crystal layer is clamped between two transparent substrates 1A and 1B, and polarizers 1C are respectively provided on the observing surface side and the back-surface side of the liquid crystal panel 1. A backlight module 3 is provided, which includes an approximately rectangular transparent light guide 2 and a light source 3A formed of an illumination module of light emitting diodes installed along a light-incident surface of the light guide 2. This backlight module 3 is provided on the back surface of the liquid crystal panel 1. Light from the backlight module 3 is deflected toward the liquid crystal panel 1 at an intermediate position, while being propagating in the light guide 2, and illuminates the liquid crystal panel 1 from the back surface thereof. A light scattering area 10 formed by dot printing or the like is provided on the back surface of the light guide 2.
Furthermore, a reflector 4 for totally reflecting light which has exited from the light guide 2 on the back-surface side thereof and for returning the light to the liquid crystal panel 1 is installed on the back side of the light guide 2. Such a bacldight 3 is stacked on the liquid crystal panel 1 with a light quantity distribution correction member such as a scattering film 12 or a prism plate (not shown), being interposed therebetween, whereby a transmission type of liquid crystal display device is constructed.
FIG. 2 is a schematic side view of the illumination module 3A of the light emitting diodes, which includes a printed circuit board 30, a one-dimensional array of light emitting diodes 31 and a plurality of resistors 32. The light emitting diodes 31 and resistors 32 are inter-disposed on the surface of the printed circuit board 30 toward the light-incident surface of the light guide 2. However, when the light emitting from the light emitting diodes 3A projects upon the light-incident surface of the light guide 2, part of the light is reflected back and absorbed by the printed circuit board 30 and the resistors 32 disposed thereon, which results in the loss of light energy. The light emitting from the illumination module 3A of the light emitting diodes 31 can not be effectively utilized, and adversely influencing the brightness and uniformity of the luminance of the backlight 3, and thus the liquid crystal display device.
Accordingly, it is an intention to provide an improved illumination module, which can alleviate the drawback of the conventional one.